1. Field of the Invention
The present invention relates to a method of forming a predetermined film on an inner surface of a tube such as various kinds of glass pipes, a capillary tube for cooling water in a nuclear device and a medical catheter for the purpose such as protection of the inner peripheral surface of the tube, and also relates to an apparatus for forming the same.
2. Description of the Background Art
In general, vapor deposition is employed for forming such a film on an inner peripheral surface of a tube.
An example of an apparatus for performing such vapor deposition will be described below with reference to FIG. 4. The apparatus shown in FIG. 4 has a vacuum container 10, in which a tube S4 to be processed (i.e., a tube on which a film is to be deposited) is disposed and held by an unillustrated holder. Inside the tube S4, there is disposed a wire-like or rod-like deposition material 90 having the same length as the tube S4. Opposite ends of the deposition material 90 are connected to a DC power source 60. An exhaust device 110 is connected to the container 10.
According to this apparatus, the exhaust device 110 operates to set an interior of the container 10 to a predetermined degree of vacuum, and the DC power source 60 applies a DC power to the opposite ends of the deposition material 90. Thereby, the deposition material 90 is heated and is vacuum-deposited onto the inner peripheral surface of the tube S4, so that an intended film is formed on the inner peripheral surface of the tube S4.
However, according to the deposition by the vacuum deposition apparatus described above, when the tube S4 has a small inner diameter, the deposition material 90 must has a small diameter corresponding to it, so that the deposition material is liable to break when it is evaporated by application of the electric power. In order to continue the deposition of the film on the inner peripheral surface of the tube, the broken deposition material must be replaced with new one. For this replacement, the container 10 must be temporarily set to the atmospheric pressure for mounting a new deposition material, and, after the mounting, the container 10 must be set to the predetermined degree of vacuum, which requires a time-consuming operation and hence reduces a productivity.
A plasma chemical vapor deposition (plasma CVD) method is a method allowing supply of a deposition material without breaking the vacuum state. This method, however, cannot generate plasma inside the tube, and cannot form a film on the inner peripheral surface of the tube. If the plasma is generated outside the tube, the plasma cannot be supplied into the tube.